Getting heat out of the rear ceiling vents.....

In a word.... NO....................................

If you remove the dash/vent thingie you will find that the rear ceiling
vents are fed by metal ductwork incorporated into the body of the van.  You
would have to do some serious cutting with a torch or something to get into
the ducts in the front of the vehicle.

Personally I haven't had a problem figuring out the heater controls, but I
had an old SAAB before the Vanagon, and SAAB's also have heating systems
with one control for heat, one for windshield air, and one for floor air,
(and on newer ones there is also one for the rear floor and one for the rear
window).  BUT my parents could never figure the Vanagon heater out...  They
also owned SAABs and were the first owners of the Vanagon!!!!!  Go
figure!!!!!!